Recently, great attention is focused on hybrid vehicles having a storage device, an inverter, and an electric motor driven by an inverter, mounted as the driving source, in addition to a conventional engine.
Japanese Patent Laying-Open No. 2005-130615 discloses a motor drive apparatus mounted on such a hybrid vehicle to drive a plurality of motor generators. The motor drive apparatus includes a DC (Direct Current) power source, a capacitor, first and second inverters driving first and second motor generators, respectively, and a control device. The control device includes first and second AND gates, and an ECU (Electronic Control Unit).
In the case where the electric power generated by the first motor generator exceeds a threshold value when the first and second motor generators are in a regeneration mode and a power running mode, respectively, in this motor drive apparatus, the ECU generates aid provides to the first AND gate a shut down permit signal to permit shut down of the first inverter. The second inverter generates a fail signal upon detecting excessive current and provides the fail signal to the first AND gate. The first AND gate takes the AND operation of the shut down permit signal from the ECU and the fail signal from the second inverter to provide a shut down signal to the first inverter.
In the case where a fail signal is output from the second inverter when the electric power generated by the first motor generator is great, the first inverter is shut down according to the motor drive apparatus. Therefore, the first and second inverters and the capacitor can be protected from damage caused by excessive voltage.
Since determination of whether the electric power generated by the first motor generator is large or not is made in software by the ECU in the aforementioned motor drive apparatus, voltage rise may occur due to delay in the operation process. A large voltage rise occurs when the regenerated power increases abruptly. Margin in the capacitor (margin in capacitance of capacitor) must be ensured in consideration of such operation delay in the motor drive apparatus, which in turn will increase the capacitor.
Furthermore, when the first inverter is shut down in response to a fail signal from the second inverter in the motor drive apparatus, the shut down of the first inverter is not canceled until the second inverter attains a proper state. Therefore, a limp-home mode (flexible form) using the first motor generator when the second inverter is in error cannot be implemented.